Solifenacin, chemically known as (3R)-1-azobicyclo[2.2.2]oct-3-yl-(1S)-1-phenyl-3,4-dihydroquionline-2-(1H)-carboxylate, and its pharmaceutically acceptable salts have highly selective antagonism to muscarine M3 receptor and are used for preventing and treating urinary diseases, such as neurogenic urinary frequency, neurogenic bladder, nycturia, unstable bladder, bladder spasm, and chronic cystitis, and respiratory diseases, such as chronic obstructive pulmonary disease, chronic bronchitis, asthma, and rhinitis. The chemical structure of Solifenacin (Cas No. [242478-37-1]) is as follows:

The process for preparing Solifenacin has been known, where the key step is connecting the isoquilinline moiety to the quinucilidinyl moiety via a carbonyl group

Major processes to obtain Solifenacin are as follow:
(1) Process where a triphosgene or phosgene is used:

According to processes disclosed in U.S. Pat. No. 6,017,927, EP0801067, and WO2005105795, triphosgene is used to introduce the carbonyl group to synthesize Solifenacin in the presence of strong base. For the reason that the highly toxic phosgene will be inevitably released in the process, extremely high requirements on environment safety are needed. At the same time, it is hard to control the impurities, in particularly, to prevent the generation of the impurity, bis((S)-1-phenyl-3,4-dihydroisoquinolin-2(1H)-yl)methanone.
(2). Process where chloroformate used

R is an alkyl or a substituted alkyl. According to processes for preparing Solifenacin as disclosed in Drugs of the future 24(8), 871-874, 1999, WO2005075474, WO2007076116, WO2008011462, and WO2008019055, chloroformates are used in the process. Even though the process prevents the generation of bis((S)-1-phenyl-3,4-dihydroisoquinolin-2(1H)-yl) methanone, the use of highly toxic chloroformates to prepare carboxylate derivatives (formula I) may cause much trouble in operation safety and environmental health.
(3). Other process
Processes disclosed in U.S. Patent Application Publication No. 20100029944 and Chinese Patent CN101711248, N,N′-Carbonyldiimidazole (CDI) and N,N′-Carbonyl-di-(1,2,3-tiazole) (CTD) are respectively used for the introduction of carbonyl group of Solifenacin. As CDI and CDT are relatively expensive and in high molecular weights, these processes are not practicably useful for industrial manufacture with high cost and low atom economy. According another process disclosed in Monatsh, Chem. (2011) 142:1181-1186, and WO2010103529, bis(p-nitrophenyl) carbonates (NPC) is used for the introduction of carbonyl group. However, NPC is not favorable to industrial application as it is irritant and harmful.